To promote the recycling and reuse of waste concrete, this study investigated the comprehensive impact of recycled aggregate (RA) content and particle size on the mechanical properties of concrete. A novel equivalence parameter (λ_eq) of RA was developed to consider the influence of RA content and size on the mechanical properties of concrete. Empirical equations were developed using linear regression to describe the test results and predict the impact of content and size of RA on the mechanical properties of concrete. The results showed that the comprehensive impact on the mechanical strength of recycled concrete shows a certain regularity when the content and particle size of RA change simultaneously. The measured mechanical properties and regression equations provided a reference and basis for engineering applications, such as the processing of RA in a crushing plant, the design of mix proportions in concrete using RA, and the rapid assessment of mechanical properties on-site. This study provides a design method and technical path for green construction.